1. Field of the Invention
This invention relates to a method for improving the transient thermal properties of air-lubricated hydrostatic bearings for the main spindles of lathes, machining centers, turning centers, and other precision machine tools.
2. Prior Art Statement
In the prior art, when precision machining is performed with various types of precision machine tools, air-lubricated hydrostatic bearings are used for the main spindle bearings. The entire machine tool is installed within a constant-temperature chamber, and the air supplied to the spindle bearings is supplied at the same temperature as the temperature within the constant-temperature chamber. This method is used to homogenize the temperature distribution of the machine tool.
A main spindle lubricated by air in this manner innately has low friction, and the lubricating air will absorb and exhaust any heat generated, so very little thermal deformation would occur. However, when extremely high precision machining is performed, even thermal deformation on the order of several .mu.m can adversely affect precision, thus requiring measures to reduce such thermal deformation.
In order to reduce this thermal deformation, the entire machine is externally cooled using oil, water, air or the like.
However, the method of external cooling of the entire machine tends to cool even unnecessary areas, requiring the addition of an inordinate amount of energy in comparison to the magnitude of the decrease in thermal displacement, thus degrading efficiency.
To solve this problem, the inventor of the present invention has proposed a method of reducing displacement by supplying the air spindle bearings with air of a temperature lower than the temperature within the constant-temperature chamber as lubricating air (Japanese Patent Application Public Disclosure No. 3(1991)-274737).
This newly proposed method can effectively reduce the absolute value of the thermal displacement in the steady state. However, this method requires a warm-up time of roughly 6-7 hours until the thermal displacement reaches the steady state, so a reduction in this warm-up time is desirable.
The present invention came about in light of the above, and its purpose is to provide a method for improving the transient thermal properties that can effectively reduce the absolute value of the thermal displacement in the steady state, and moreover, can shorten the warm-up time until the thermal displacement reaches a steady state.